Holes can be drilled in rock by utilizing rotary drilling or down-the-hole drilling (DTH). A rotary drilling machine and a DTH drilling machine both include a rotation unit for rotating a drilling tool. The rotation unit includes a shaft that is rotated around its longitudinal axis. Rotation and torque is generated by one or more rotating motors connected to the shaft through a gear system or transmission members. During the drilling operation the rotation unit is fed axially by means of a feed device in a drilling direction and return direction. Thus, the shaft of the rotation unit is subjected to rotational and axial forces.
The shaft is supported to a body of the rotation unit by means of bearings. Proper operation of the bearings require that clearances of the bearings are inside predetermined limits. Further, the bearings often require use of a defined pre-load. However, the bearing clearance and the pre-load change when the bearings settle during use after the installation and when the bearings are subjected to wear. Therefore, the bearing clearance and the pre-load needs to be checked and adjusted according to a service plan. Structures of the known rotation units require complicated and time-consuming measures for executing the needed service.